So why in the world can’t Mayor Bloomberg and Police Commissioner Ray Kelly?

Bridgeport Mayor Bill Finch says The Post’s call for police departments to stop buying Glock sidearms until the company stops general sales of 30-round magazines — like the one used in the Tucson massacre — is “an excellent idea.”

Indeed, he said, he’s already spoken to his own chief of police about making it happen.

“I’ve been to too many funerals of young people killed in gun violence,” said Finch. “We have to restrict these powerfully violent weapons.”

Finch, it should be noted, is a member of Mayors Against Illegal Guns, the nationwide group co-chaired by Bloomberg and Boston Mayor Thomas Menino.

Which makes the less-than-energetic response from New York’s City Hall and 1 Police Plaza all the more disappointing.

Bloomberg calls it “an interesting idea” and says he’ll raise it — whenever — with that group of mayors.

On the other hand, Public Advocate Bill DeBlasio — with whom this page is rarely in agreement — has endorsed The Post’s call.

“If Glock will not stop selling these magazines to consumers,” he said, “then the New York Police Department should start buying the firearms they need from a different company.”

Commissioner Kelly says the NYPD has always opposed the sale of high-capacity magazines “regardless of manufacturer” and has called for a federal ban.

But he notes that the city already buys weapons from two other producers besides Glock — and that all three sell high-capacity magazines, as do other manufacturers.

Were the NYPD to boycott a particular manufacturer, said a spokesman, “there [eventually] would be no source of reliable weapons for any newly hired officer.”

We see the point, but that’s not good enough.

Someone needs to be made an example of — and Glock, which manufactured and sold the murder weapon used in Tucson — is the one most prominent right now.

If Glock can be pressured into changing its policy, we suspect other companies will follow suit — by means of a nationwide boycott by police departments against them, if necessary.

But someone has to take the lead.

And there’s no one more appropriate than Bloomberg and Kelly, who run the nation’s largest — and best — municipal police department.